Legume "Little leaf", a virus disease of subtropical pasture species

Abstract

A virus of legumes causing a disease described as "little leaf" has infected with differing degrees of severity some 40 per cent. of pasture legumes in experimental plots in subtropical Queensland. The symptoms are similar to those caused by the "big bud-witches' broom" complex of viruses of which it is probably another strain. Transmission studies have shown that the vector is the leafhopper Orosius argentatus (Evans) which also transmits tomato "big bud", lucerne "witches' broom", potato "purple top wilt", and tobacco "yellow dwar"' diseases. The O. argentatus taken direct from the field in Queensland, and its progeny reared in the laboratory, were efficient vectors of "little leaf" whereas the Canberra strain bred in the laboratory would not transmit 'little leaf' and was not an efficient vector of the other "yellows" viruses. The majority of species and strains tested in the genera Crotalaria, Desmodium, Indigofera, and Stylosanthes are susceptible to "little leaf". Within such genera there are a few resistant species or strains with promising agronomic characters. Lucerne and white clover are relatively resistant to "little leaf". The genera Arachis, Centrosema, Doliehos, Glycine, Lespedeza, Leucaena, Pueraria, Phaseolus, Vigna, and Zornia contain species and strains with marked field resistance. Most of the species and strains considered to be promising pasture legumes possess field resistance to "little leaf".